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United States Patent |
5,199,884
|
Kaufman
,   et al.
|
April 6, 1993
|
Blind mating miniature connector
Abstract
A surface mounted connector (25) for interconnecting closely centered
circuits such as those carried by circuit boards (12, 18) includes plug
and receptacle housings (24, 90) which internest to interconnect edge
mounted, thin stamped contacts (50, 116) on centers complementary those of
said circuits which include a contact configuration producing a series of
point contacts (70, 128) and solder wells (70, 130) to provide an improved
solder joint between respective contacts and boards. The contacts extend
outside the side walls of the housings (64, 164) to facilitate heat
application for solder reflow and inspection of solder joints. The
contacts further have barbs (66, 126) engaging the said housings to hold
the contacts against displacement upon separation of the plug from the
receptacle. Solder pads (76) are provided on each housing to mechanically
hold the housing to a board, and the plug housings include bevels (34) and
polarizing and aligning plastic posts (44) which fit in recesses (96) in
the receptacle to facilitate blind mating with latching surfaces (48, 100)
latching the plug and receptacle together. A method is taught which
features a tapering of beam lengths of the plug contact (50) to reduce
stress and optimize force and/or deflection characteristics.
Inventors:
|
Kaufman; John W. (Hershey, PA);
Summers; Donald J. (Shiremanstown, PA);
Pratt; Gregory R. (Etters, PA)
|
Assignee:
|
AMP Incorporated (Harrisburg, PA)
|
Appl. No.:
|
801561 |
Filed:
|
December 2, 1991 |
Current U.S. Class: |
439/74; 439/80; 439/83; 439/566; 439/570; 439/676 |
Intern'l Class: |
H01R 009/09 |
Field of Search: |
439/64,74,76,78-81,83,660,677,680
|
References Cited
U.S. Patent Documents
3960434 | Jun., 1976 | Soes | 339/176.
|
4479686 | Oct., 1984 | Hoshino et al. | 339/17.
|
4616893 | Oct., 1986 | Feldman | 439/83.
|
4678121 | Jul., 1987 | Douty et al. | 439/83.
|
4734060 | Mar., 1988 | Kawawada et al. | 439/660.
|
4869677 | Sep., 1989 | Johnson et al. | 439/80.
|
4929185 | May., 1990 | Wong et al. | 439/74.
|
4971565 | Nov., 1990 | Fox | 439/74.
|
5030107 | Jul., 1991 | Moon | 439/62.
|
5057027 | Oct., 1991 | Yamada et al. | 439/83.
|
5104324 | Apr., 1992 | Grabbe et al. | 439/83.
|
Foreign Patent Documents |
1268247 | May., 1968 | DE.
| |
424905 | May., 1967 | CH.
| |
Primary Examiner: Bradley; Paula A.
Claims
We claim:
1. A miniature electrical connector for interconnecting circuits on close
centers on the surfaces of circuit boards including plug and receptacle
housings each having arrays of contacts of thin sheet metal set on edge in
such housings on centers complementary to the centers of the circuits and
including contact feet projecting from said housings in a common plane for
soldering to said circuits with the receptacle housing including an
interior cavity configured to receive the plug housing inserted therein
along a given axis and with the plug housing having a bevel to ease entry
into said cavity and having interior recesses containing said plug
contacts therewithin positioned to receive said receptacle contacts
entering said recesses to engage said plug contacts in a sliding
engagement, where said contact feet include a U-shaped configuration with
a locking point interiorly of the U-shaped configuration adapted to bite
into the housing to hold the contact relative to the housing, and said
plug and receptacle contacts each have ends opposite said feet positioned
to be deflected transversely to said axis during such engagement to
develop low resistance, stable electrical interfaces, said plug housing
including a plurality of posts projecting from a front face thereof and
the receptacle housing including interior recesses positioned to receive
said posts to polarize and align said housings to assure entry of the
receptacle contacts into the recesses of the plug housing and facilitate
blind mating of said housings.
2. The connector of claim 1 wherein said contact feet include a plurality
of contact points spaced apart to engage a board at two points and to
define a well therebetween increasing the contact surface area and volume
of solder between the contact and the circuits of the board.
3. The connector of claim 1 wherein said contact feet extend outwardly from
the sides of the said housing to facilitate inspection of the positioning
of a housing relative to the circuits of a circuit board and the
application of heat to effect solder reflow with the resulting solder
joints being visually observable.
4. The connector of claim 1 wherein the contacts of the plug include a J
profile having a contact surface on the end thereof.
5. The connector of claim 1 wherein said posts and recesses include
latching surfaces to latch the housings together upon the plug half
housing being fitted into the receptacle housing.
6. A miniature electrical connector for interconnecting circuits on close
centers on the surfaces of circuit boards including plug and receptacle
housings each having arrays of contacts of thin sheet metal set on edge in
such housings on centers complementary to the centers of the circuits and
including contact feet projecting from said housings in a common plane for
soldering to said circuits with the receptacle housing including an
interior cavity configured to receive the plug housing inserted therein
along a given axis and with the plug housing having a bevel to ease entry
into said cavity and having interior recesses containing said plug
contacts therewithin positioned to receive said receptacle contacts
entering said recesses to engage said plug contacts in a sliding
engagement, where the housings of the plug and receptacle each include
metallic fasteners extending from the surfaces thereof and positioned to
engage a circuit surface and be soldered thereto to hold said housings to
the respective circuit boards, and said plug and receptacle contacts each
have ends opposite said feet positioned to be deflected transversely to
said axis during such engagement to develop low resistance, stable
electrical interfaces, said plug housing including a plurality of posts
projecting from a front face thereof and the receptacle housing including
interior recesses positioned to receive said posts to polarize and align
said housings to assure entry of the receptacle contacts into the recesses
of the plug housing and facilitate blind mating of said housings.
7. The connector of claim 6 wherein the said fasteners include flat
surfaces to effect a solder connection to the flat surfaces of metallic
pads of a board surface.
8. The connector of claim 7 wherein each of said fasteners includes a
projection having a latch thereon fitting into a housing to hold a said
fastener to the housing.
Description
This invention relates to an electrical connector for blind mating to
interconnect circuits such as printed circuit boards and a method for
making contacts.
BACKGROUND OF THE INVENTION
In U.S. patent application Ser. No. 07/675,839 filed Mar. 7, 1991, and
drawn to a surface mount connector, there is disclosed an extremely small
electrical connector for interconnecting the circuits of circuit boards
and the like. The connector there disclosed is capable of being rendered
in an extremely miniature size, for example, for circuit traces having a
pitch on the order of 0.5 mm and is adapted for surface mounting to boards
which in turn carry components interconnected by the connector. Such
connectors are particularly adapted for use with small electronic devices
such as cameras, video cameras, and other relatively compact and densely
packaged electronic products. At least in one application wherein
component carrying boards are interconnected in parallel, the connector
cannot be physically held as it is soldered to the surface of the board
and plugged into a connector half soldered to the surface of an opposing
board. The connection must be mated "blind," meaning that an installer
cannot see the connector or hold the connector, but must rely upon the
connector itself to facilitate mating, unmating being less of a problem.
In addition to the difficulty of mating, the small, relatively delicate
portions of the plastic and metal parts of a connector make damage from
stubbing or mismating a definite problem.
It is, accordingly, an object of the present invention to provide an
improvement for miniature electrical connectors which require blind
mating. It is a further object to provide a miniature blind mating
connector for interconnecting circuits of the type utilized on the
surfaces of circuit boards, having extremely close center-to-center
conductive trace spacings. It is a still further object to provide a
surface mounted connector having features facilitating blind mating and
alignment with circuit traces for surface mount soldering to circuit
boards and the like.
It is a final object to provide a method of making spring contacts that
minimizes stress and better controls contact force relative to deflection.
SUMMARY OF THE INVENTION
The present invention achieves the foregoing objectives through the
provision of a connector having plug and receptacle housings wherein the
plug housing fits within the receptacle housing and the contacts of the
plug are recessed within the housing of the plug to be engaged by the
contacts fitted in the housing of the receptacle, which is relieved to
receive the plug. The connector of the invention includes contacts placed
on close centers such as on the order of 0.5 mm (0.020 inches) to provide
a high density interconnection. The housings of the connector include
intermating surfaces defined by posts extending from the plug housing and
recesses interiorly of the receptacle housing which polarize and align the
connector halves for intermating. The plug housing is beveled to enter the
receptacle housing in a precise way thereby preventing stubbing and
mismating of the delicate contacts entering recesses of the housings
during mating and, in spite of the necessity for blind mating.
The housings of the invention also include fasteners attached thereto and
solderable to the printed circuit board surfaces to which the connector
halves are attached to hold the connector halves to the boards and align
the contacts therein with traces on the board. The contacts of the plug
and receptacle halves are stamped of thin, spring grade metal to be set on
edge in the housing recesses so as to be freestanding and capable of
deflection within the housings, clear of the housing walls, in a sense
transverse to the axis of engagement of plug and receptacle. This feature
allows a normal deflection easing tolerances and assuring a substantial
normal force engagement to assure a sufficient force to maintain a stable,
low-resistance electrical interface between contacts when mated. The
contacts of the receptacle include a straight post portion free standing
for deflection. The contacts of the plug include a J-shaped spring portion
and a method for making such contacts to have beams tapered in a novel way
to maintain sufficient normal force, which assures stable electrical
interface for a given deflection as well as minimizing stress. Each of the
contacts, plug and receptacle, include projections which have barbs
engaging the plastic of the housings to latch and lock the contacts to the
housings there by minimizing displacement thereof. Each of the contacts
further includes a foot extending outwardly of the housing and containing
points projecting to define a solder well to both extend the surface area
of a solder joint and allow the welling of a fillet broadening the solder
contact surfaces with the circuit of a board to the contact. This feature
facilitates an easy visual examination of the connector prior to soldering
to make certain of alignment on the board surface, the ready application
of heat to the contacts to effect a solder reflow, including heat sources
of the infrared type, in addition to the usual types of heat application
and, finally, a ready inspection of the solder fillet following reflow.
The contacts include relatively smooth edge surfaces that intermate with a
relatively low force of engagement and disengagement, in a sliding
movement. Latching of the connector halves together is accomplished by the
provision of latching surfaces on the posts of the plug half with surfaces
within the receptacle half when the halves are fully intermated.
IN THE DRAWINGS
FIG. 1 is a perspective view of the connector of the invention,
considerably enlarged, with the plug and receptacle halves joined to
circuit boards shown partially in phantom, prior to intermating.
FIG. 2 is a perspective view, partially in phantom, showing the connector
of FIG. 1, and the circuit boards thereof, intermated.
FIG. 3 is an elevation view, in partial section, showing the connector of
the invention, aligned for, but just prior to, mating.
FIG. 4 is a view similar to FIG. 3 but with the connector halves
intermated.
FIG. 5 is an elevation and partially sectioned view of the connector halves
aligned, but prior to mating, showing the details of the alignment posts
and latching surfaces.
FIG. 6 is a view of the connector shown in FIG. 5 but intermated.
FIG. 7 is a detail of the fastener latching within the housing of a
connector half taken along lines 7--7 of FIG. 6.
FIG. 8 is a perspective view of a contact utilized with the plug half of
the connector of the invention.
FIG. 9 is a perspective view of a contact utilized with the receptacle half
of the invention.
FIG. 10 is a perspective view of the contact of FIG. 9 showing a further
aspect of the invention related to stress reduction.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, an assembly 10 includes a pair of circuit boards
12 and 18. These boards may be taken to be sections of much larger boards
that carry components and interconnections to provide an electronic
function for an electronic device. As can be appreciated from the views in
FIG. 1 and FIG. 2, the connector 25, including the plug and receptacle
halves 24 and 90, must be blind mated to interconnect, the position of the
connectors in fact making it impossible for an operator to handle the
connectors 25 themselves. To provide context, the stack heights or
dimension between the inner surfaces of the boards 12 and 18 when the
connector halves 24,90 are plugged together, as shown in FIG. 2, is on the
order of 5 mm, or 0.197 inches for one size of connector, and 4 mm, or
0.157 inches for a smaller size connector. To intermate the connector
halves, an installer must grasp one of the boards, such as board 18, shown
in FIGS. 1 and 2, and push it toward the other board, such as board 12
until the connector halves engage and are intermated with the plug half 24
entering into the receptacle half 90.
In accordance with the invention, each of the boards 12 and 18 have
respective circuit pads 14,22, as seen in FIGS. 3 and 4, which
interconnect to corresponding contacts in connector halves 24,90 and
circuit traces (not shown) thereon extending over the surfaces of the
boards to interconnect to components or other circuits, either on the
surface of the boards or within the boards, including layers within such
boards. Additionally, pad-like surface traces 16 are provided on the
surface of board 12 and pad-like surfaces 20 are provided on the
undersurface of board 18 as shown in FIGS. 1 and 2. These conductive
traces are not connected to any electrical circuit, but serve to assist in
aligning the connector halves 24,90 with respect to the conductor traces
on the boards and facilitate a mechanical holding of the halves by being
soldered to fasteners that are part of each connector half in a manner to
be described. The plug half 24 of the connector includes a plastic housing
26 that has a floor 28 and a portion 30 extending therefrom. A series of
recesses 32 are provided, extending through floor 28 and up along the
portion 30 to receive and accommodate contacts fitted in the housing. As
can be discerned in FIG. 1, and in more detail in FIG. 3, the upper
portion 30 of the housing 26 includes a bevel 34 which facilitates blind
entry of the plug half 24 into the receptacle half 90. As shown in FIG. 3,
the beveled portion 34 leads to an outer side wall 36. Interiorly of the
recesses 32 is a dividing wall 38, shown in FIG. 3, and outside edge
portions 40 of the floor 28 that include outside surfaces 42 engaged by
portions of the contacts 50 to lock the contacts 50 to the housing 26 in a
manner to be described. As can be seen in FIG. 1 and in more detail in
FIGS. 5 and 6, the plug housing 26 includes alignment posts 44, beveled at
the ends as at 46 which protrude beyond the portion 30 of the connector
housing and are formed integrally with the housing when it is molded. The
alignment posts 44, stationed proximate the ends of the housing 26, also
include a latch 48 which is shown in detail in FIG. 5 and in engagement in
FIG. 6 with surfaces 100 of the receptacle. As can be seen in FIG. 5, the
posts 44 project well above the end surface 39 of the housing 26.
Each of the housing halves further includes at the ends a recess to receive
a fastener, fasteners 76 shown in FIGS. 1 and 5. The recesses include, in
the plug half 24 shown in FIG. 5, a passage 43 and a bevel 45 facilitating
the insertion of the fastener 76. The receptacle half includes a passage
13 with a bevel 115.
Referring now to FIG. 3, the housing 26 includes two rows of contacts 50
inserted therein. As can be appreciated, these contacts, also shown in
FIG. 8, are flat metal stampings having a profile defining a variety of
contact characteristics. These contacts 50 are, in essence, set on edge
and inserted into the housing 26 from the bottom thereof through a portion
of floor 28 to extend within the recesses 32. Each of the contacts 50 has
a base or foot portion 52 with an upstanding spring portion 54, a bend 56,
a downwardly projecting portion 58, and a rounded end portion 60.
Extending from the base portion 52 is a further portion 62 which, together
with an upstanding leg 64, defines the position of a barb 66 internally
directed in a relief 68 shown in FIG. 8 in the base or foot 52 of the
contact 50. As can be seen in FIG. 3, when the contact 50 is loaded into
the housing, the barb 66 bites into the surface 42 of the floor 28 to lock
the contact to the housing. Note in FIG. 3 that the wall portion 40 limits
the insertion of the contact 50 within the housing in one direction with
the barb 66 limiting displacement of the contact 50 in an opposite
direction. Additionally shown in FIG. 8 and in FIG. 3 are details of the
foot 52 of the contact 50 which facilitate soldering to the circuit trace
22 of board 18. The contact portion 52 includes a pair of rounded points
70, which are spaced apart to define a well 72 intended to accommodate a
fillet of solder upon reflowing of solder between the trace 22 and the
contact 50. FIG. 4 shows the mated connector halves with solder fillets S
appropriately reflowed to interconnect the contacts of the connector to
the traces of the printed circuit boards 12 and 18 and the traces 14 and
22 of such boards. As can be appreciated, the points 70 defined by curved,
rounded surfaces including the well 72 increase the surface area, the edge
surface area of the contacts, as well as defining a body of solder
extending along the surfaces to thus broaden the contact area between
solder and contact. It has been discovered that wells provided at the
interface of solder joints not only mechanically strengthen the interface
through providing an additional volume of solder as well as an additional
surface area, but improve the electrical characteristics as well. Using
points such as 70 rather than flat surfaces also controls precisely the
point of contact between surfaces.
To be noted in FIG. 3, the contact 50 is positioned within the housing 26
so as to be freestanding, with respect to the spring end, the J portion of
the contact 50. Also to be noted is the action of the barb 66 in holding
the contact 50 rigidly within the housing 26 with a clearance sufficient
to permit a deflection of the contact 50 in the manner shown in FIG. 4
when engaged with the opposing contact 116 of the receptacle half 90. The
invention contemplates that the contacts 50 may be formed by stamping a
thin sheet metal stock such as phosphor bronze on the order of 0.008
inches in thickness of considerable hardness, such as a hardness of 10 M.
The J portion of the contact in a prototype design had a height on the
order of 0.111 inches as measured between the root of the spring and the
top of the bend. The overall height of the contact was on the order of
0.160 inches.
As can be appreciated from the view shown in FIG. 3, the J portion of
contact 50, including portions 54, 56, 58, and 60 reside in a relaxed
state within the profile of the housing 26, the ends 60 extending within
recess 32 proximate to the surface 36 forming the side wall of the housing
26. In this way, the relatively delicate contacts 50 are protected from
damage and handling following manufacture and prior to use. Also to be
noted with respect to the showings in FIGS. 3 and 4, is the fact that the
base portions 52, including the points 70, well 72, and portions 64 extend
out from the edge of the housings 26 to be readily visible in the manner
shown in FIG. 2. This allows an inspection of the connector halves,
resting upon the surface of their respective boards, prior to soldering
and following soldering. Moreover, it allows the use of heat to readily
get to the contacts 50 to cause a solder reflow, including particularly
infrared heat, which will strike the projecting portions of the contacts
to effect solder reflow. In practice, the plastic of the housings should
be made of a material capable of withstanding the heat associated with
solder reflow, high temperature surface mount plastics of a type having
little shrinkage and bowing with easy to flow thin walls are preferred. A
Eastman Kodak material Ektar-CG907-8906-C or a material Vectra-E130 from
Hochst-Celanese are examples of such materials.
FIGS. 5, 6, and 7 show the application of the fasteners 76 heretofore
mentioned, reference being made to the fasteners utilized with both plug
and receptacle halves 24,90. In FIG. 5, a fastener 76 may be seen to
include a flat pad surface 78 joining an upturned projection 80 with the
fastener positioned for insertion within the passage 113 guided by bevel
115 formed in the housing 91 of the receptacle half 90. FIG. 6 shows the
fastener 76 in place, and FIG. 7 shows the portion 80 of the fastener 76
includes projections or barbs 82 which bite into the material of the
housing 91 to lock the fastener 76 in place in the position shown in FIG.
6 and also in FIGS. 1 and 2. The fasteners 76 can be visually aligned with
appropriate traces 16,20 on the boards 12 and 18 prior to solder to help
position the halves 24,90 properly on the board surfaces. An appropriate
solder paste or other means of providing solder between the pads 76 and
appropriate traces on the boards may be provided to result in a solder
reflow with the pads mechanically joining and fixing the connector halves
to the boards.
FIGS. 5 and 6 also show the operation of the aligning and polarizing post
44, FIG. 5 showing the halves 24,90 prior to insertion and mating, and
FIG. 6 showing the halves 24,90 following mating. As can be discerned, the
surface latches 48 enter recesses 96 in the receptacle half 90 and engage
interior surfaces 100 in such housings to hold the halves 24,90 intermated
together and preclude an accidental withdrawal. The dimensions of the
surfaces on latch 48 and the surfaces 100, relative to the elasticity of
the plastic of the housings, is made so that the housings can be, in
essence, peeled or pulled apart by drawing the two boards 12 and 18
relatively apart. To be noted in FIGS. 5 and 6 are the bevels 46 provided
on posts 44 and the bevels 98 provided on recesses 96 which facilitate the
blind intermating of the connector halves.
Referring now to FIG. 1, the receptacle half 90 includes housing 91 having
an interior cavity 92 which is dimensioned to receive in an easy sliding
fit, the portion 30 of housing 26 from plug half 24, the beveled portions
34 thereof, easing the insertion of the plug half 24 within the receptacle
half 90 in terms of alignment. The receptacle half 90 further includes
ports 94 in the end side walls, which allow flow of air during mating and
unmating to prevent air pressure from restricting manipulation of the
housing halves 24,90. Receptacle half 90 includes a housing 91 of plastic
material similar to that of the plug half 24. The housing 91 includes
interiorly a series of recesses 102, as shown in FIG. 1. FIG. 3 shows the
interior of housing 91 includes a series of apertures 104 allowing
admission of the contacts 116 and further includes a floor 106 and
exterior walls 108. To be noted is the interior surface of such walls,
shown as 110, which is spaced from the contacts 116 to facilitate slight
deflection of the post portion of the contacts for purposes to be
described hereinafter. To be noted is the surface 112 on the exterior of
the housing 91 which is engaged by a barb 126 of contact 116 to lock the
contact 116 to the housing 91 in the manner described with respect to the
plug half 24. FIG. 9 shows the contact 116, which is formed of a material
similar to that of the contact 50, heretofore described, to include a post
portion 118 rounded at 120, including a base or foot 122 having an
upwardly projecting portion 124 ending in barb 126. The contact 116
includes points 128 defining a solder well 130 similar to that heretofore
described with respect to the contacts 50.
As can be seen in FIG. 1, the post portions 118 of contacts 116 extend into
cavity 92 exteriorly of the recesses 102 and are positioned to enter the
recesses 32 in plug half housing 26 and engage the contacts 50 therein,
the contact surfaces 60 engaging the edge surfaces of the post portions
118 in the manner shown in FIG. 4. This required entry of the post
portions 118 into the recesses 32 of the plug half housing 26 further
assures an appropriate alignment. To be noted is the fact that the
surfaces of portion 118 are smooth to be engaged in a sliding movement
with the surfaces 60 limiting the force of engagement as the contacts
50,116 are intermated together. Also to be noted is the fact that the
surfaces 60 achieve a substantial smooth wipe along the edge and length of
post portions 118. At the time the contacts 50,116 are intermated, the
contacts 50,116 will have been soldered to their respective boards 18,12
to preclude movement of the contacts 50,116 which would reduce the
deflection and normal force there between. This normal force is desirable
to include a force sufficient to maintain a low, stable, electrical
resistance between the contacts 50,116.
As an additional aspect of the invention, we have discovered that by
providing a tapering of the beam of contact 50 changes in normal force can
be achieved as well as reductions in maximum stress in the elastic region
and stress induced failure and set. In FIG. 10 the contact 50 is shown
with the various leg portions 54, 55 and 58 given length dimensions
1.sub.1, 1.sub.2 and 1.sub.3 with each of the leg portions tapered. The
leg portion 54 tapers inwardly, from the base B to a point joining leg
portion 55 that tapers outwardly to a point where the leg portion 55 joins
bend 56. The leg portion 58 tapers inwardly, from the bend 56 to just
proximate the enlarged end defining contact surface 60. By virtue of the
tapers stress in the contact induced by deflection D developed by a force
F due to mating engagement with contact 116 is distributed along the beams
reducing the maximum stress in bend 56 and at the base B as compared to a
non-tapered beam. The taper of leg portion 58 similarly distributes the
stress along that beam reducing the maximum stress in the bend B.
The following is an example of the use of a tapered beam width to achieve
the design goal to maintain sufficient normal force, which assures the
electrical integrity of the interface, while reducing maximum elastic
stress limits for a defined deflection. In a contact 50 of constant beam
width on the order of 0.011 inches in a 10 M hard phosphor bronze material
0.008 inches thick and an overall height L of 0.160 inches, the maximum
elastic equivalent stress was 223,900 p.s.i. occurring proximate base B
for a maximum deflection of 0.008 inches. A contact of the same material
and thickness with the same deflection having a taper from 0.011 inches to
0.009 inches for 1.sub.1 and from 0.009 inches to 0.0124 inches for
1.sub.2 and 1.sub.3 reduced the maximum elastic stress to 183,500 p.s.i.;
1.sub.1 being 0.00546 inches, 1.sub.2 being 0.0354 inches and 1.sub.3
being 0.030 inches in length. This demonstrates a 22% reduction in the
maximum stress while the normal force was maintained ar a reasonably high
level. The non-tapered contact developed a normal force F of 0.441 pounds
and the rapiered version developed a normal force F of 0.445 pounds for a
maximum deflection of 0.008 inches. Additionally, in the constant width
example, for a deflection of 0.0055 inches, the normal force F developed
was on the order of 0.302 pounds and the normal force for the tapered
version was 0.306 pounds. The maximum stress for the non-tapered beam is
153,959 p.s.i. and for the tapered version is 126,171 p.s.i. at the given
nominal deflection.
By altering the lengths of tapers, stress can be distributed and maximum
stress reduced. By providing tapers, the normal force of contact can be
altered, raised or lowered, thus better controlling this vital parameter
of contact performance.
While the foregoing examples are tied to a control of width through tapers,
the invention fully recognizes that variation of cross-sectional area
along the beam length by adjusting width or thickness dimensions can
achieve a similar result although width control best lends itself to
traditional stamping and forming processes used for contacts such as 50
and 116.
In summary, the various features of the contacts 50,116, including the
alignment posts 44 and the various beveling relative to the ends of the
alignment posts 44 and the housing recesses 96, the bevel 34, the locking
by the respective barbs of the contacts to the housing, and the soldering
of the contacts to the boards, all achieve a positioning of the connector
halves 24,90 and contacts 50,116 to facilitate ready blind mating of the
contact halves 24,90 to interconnect the circuits of the boards. The
increased area and provision of wells at the solder joints facilitates a
good, low resistance solder connection between contacts and circuits, and
the provision of fasteners which are soldered to the board further
stabilizes the mechanical holding of the connector halves to the boards.
The contacts 50 include a tapering to reduce stress and allow optimization
of force and or deflection for given beam lengths and a method for making
electrical contacts.
Having now described the invention in relation to drawings of various
embodiments, claims are appended, intended to define what is inventive.
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